gnome-shell crashes at startup - segfault in nouveau_dri.so

With a live USB stick or a freshly installed version of 18.04, gnome-shell crashes at startup. I get this error in dmesg:

gnome-shell[xxxx]: segfault at xx ip xx sp xx error 4 in nouveau_dri.so[xxxx]

The computer is a MacBook Pro with a GeForce 320M GPU. Using the proprietary driver listed in the "additional drivers" tab doesn't work either (I get a black screen at startup with no access to a virtual terminal).

Everything was fine on 16.04, with nouveau or nvidia drivers.

The only workaround is to blacklist the nouveau driver. I have of course very poor performance then.

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: libgl1-mesa-dri 18.0.0~rc5-1ubuntu1
ProcVersionSignature: Ubuntu 4.15.0-20.21-generic 4.15.17
Uname: Linux 4.15.0-20-generic x86_64
NonfreeKernelModules: wl
ApportVersion: 2.20.9-0ubuntu7
Architecture: amd64
BootLog: Error: [Errno 13] Permission non accordée: '/var/log/boot.log'
CompositorRunning: None
CurrentDesktop: ubuntu:GNOME
Date: Sun Apr 29 01:34:38 2018
DistUpgraded: Fresh install
DistroCodename: bionic
DistroVariant: ubuntu
DkmsStatus: bcmwl, 6.30.223.271+bdcom, 4.15.0-20-generic, x86_64: installed
ExtraDebuggingInterest: Yes, including running git bisection searches
GraphicsCard:
 NVIDIA Corporation MCP89 [GeForce 320M] [10de:08a0] (rev a2) (prog-if 00 [VGA controller])
   Subsystem: Apple Inc. MCP89 [GeForce 320M] [106b:00c2]
InstallationDate: Installed on 2018-04-28 (0 days ago)
InstallationMedia: Ubuntu 18.04 LTS "Bionic Beaver" - Release amd64 (20180426)
MachineType: Apple Inc. MacBookPro7,1
ProcEnviron:
 TERM=xterm-256color
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=fr_FR.UTF-8
 SHELL=/bin/bash
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-4.15.0-20-generic root=UUID=8a41bdcd-9c0e-41b3-8111-94661a72e400 ro quiet splash vt.handoff=1
SourcePackage: mesa
UpgradeStatus: No upgrade log present (probably fresh install)
dmi.bios.date: 06/01/10
dmi.bios.vendor: Apple Inc.
dmi.bios.version: MBP71.88Z.0039.B0B.1006012305
dmi.board.name: Mac-F222BEC8
dmi.board.vendor: Apple Inc.
dmi.chassis.type: 10
dmi.chassis.vendor: Apple Inc.
dmi.chassis.version: Mac-F222BEC8
dmi.modalias: dmi:bvnAppleInc.:bvrMBP71.88Z.0039.B0B.1006012305:bd06/01/10:svnAppleInc.:pnMacBookPro7,1:pvr1.0:rvnAppleInc.:rnMac-F222BEC8:rvr:cvnAppleInc.:ct10:cvrMac-F222BEC8:
dmi.product.family: MacBook Pro
dmi.product.name: MacBookPro7,1
dmi.product.version: 1.0
dmi.sys.vendor: Apple Inc.
version.compiz: compiz N/A
version.libdrm2: libdrm2 2.4.91-2
version.libgl1-mesa-dri: libgl1-mesa-dri 18.0.0~rc5-1ubuntu1
version.libgl1-mesa-glx: libgl1-mesa-glx 18.0.0~rc5-1ubuntu1
version.xserver-xorg-core: xserver-xorg-core 2:1.19.6-1ubuntu4
version.xserver-xorg-input-evdev: xserver-xorg-input-evdev N/A
version.xserver-xorg-video-ati: xserver-xorg-video-ati 1:18.0.1-1
version.xserver-xorg-video-intel: xserver-xorg-video-intel 2:2.99.917+git20171229-1
version.xserver-xorg-video-nouveau: xserver-xorg-video-nouveau 1:1.0.15-2